Temperature compensation for a magnetostrictive transducer



1, 1956 M, L. DOELZ ET AL 2,760,168

TEMPERATURE COMPENSATION FOR A MAGNETOSTRICTIVE TRANSDUCER Filed Aug. 16, 1952 Maqnefosfricflue Maferials haw/pg thermoe/asfic cpefflcien is of oppqsue olar/h;

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34/111 1AM Mar/277N670 ArrakAa-r United States Patent TEMPERATURE CONIPENSATION FOR MAGNETOSTRICTIVE TRANSDUCER Melvin L. Doelz, Glendale, and William E. Whittington, North Hollywood, Calif., assignors to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application August 16, 1952, Serial No. 304,672

3 Claims. (Cl. 333-71) This invention relates in general to electromechanical filters, and in particular to temperature compensating means for maintaining the resonant frequency of a magnetostrictive transducer.

The co-pending application of Melvin L. Doelz, Serial No. 248,011, filed September 24, 1951, entitled Mechanical Filters, now Patent No. 2,717,361, issued September 6, 1955, discloses an electromechanical filter wherein a plurality of discs are coupled together and driven by an input magnetostrictive transducer. An output is removed from the filter by means of an output magnetostrictive transducer. These input and output magnetostrictive transducers are hereinafter termed the filter input and output end Wires. Electrical energy is coupled to and from the end wires with magnetic coils. Adjacent to each coil is mounted a biasing or polarizing magnet for accomplishing the magnetostrictive effect.

Each input and output end wire must be cut to a definite length so that it Will resonate at a particular frequency. As disclosed in the above mentioned Doelz application, these end wires have a length that is an oddinteger multiple of one-quarter wavelength at the resonant frequency. If the resonant frequencies of the end wires of a filter vary beyond certain limits, the filter characteristics are impaired. Temperature changes cause variations in end wire resonant frequencies. The changes in resonant frequency brought about by the thermoelastic coefiicient of materials suitable for filter end wires are of a much greater magnitude than the resonant frequency changes caused by thermal expansion.

It is an object of this invention, therefore, to provide means for minimizing changes in the resonant frequencies of end wires when subjected to temperature changes.

Further objects, features and advantages of this invention will become apparent from the following description and claims when read in view of the drawings, in which:

Figure 1 is a side view of the completed filter assembly.

Figure 2 is an enlarged sectional view of the coil assembly through the median vertical longitudinal plane illustrating the input end wire and its immediate filter components.

Figure 1 shows a base plate upon which are mounted mounting blocks 11 and 12. Cylinders 13 and 14 are supported by mounting blocks 11 and 12, and end discs 16 and 17 are firmly connected to the cylinders 13 and 14. A plurality of discs 18 are supported between the discs 16 and 17 by longitudinal coupling wires 19 that are attached to the peripheries of the discs.

An input end wire 21 extends within the hollow confines of cylinder 13 and an output end wire 22 extends within the hollow confines of cylinder 14.

As best shown in Figure 2, the disc 16 is formed with an opening 20 adjacent the lower edge so that the wire 21 may extend therethrough. Likewise, the disc 17 is 2,760,168 Patented Aug. 21, 1956 formed with an opening to allow the wire 22 to extend therethrough.

Biasing or polarizing magnets 23 and 25 are supported by mounting blocks 11 and 12, respectively. The cylinders 13 and 14 may be made of copper, which is nonmagnetic and thus does not shield the wires 21 and 22 ing 36% nickel.

It is known that most materials change their thermoelastic coefficients with temperature changes. It is proposed to fabricate the wires 21 and 22 by joining sections 34 and 35 so that the total lengths of wires 21 and 22 will be such that they will resonate at the desired frequency. By making one section 34 of a material which has a negative thermoelastic coefiicient and the other 35, of a material which has a positive thermoelastic coetlicient, a constant resonant frequency of the wires 21 and 22 may be maintained over a considerable temperature range.

The sections 34 and 35 will be chosen so that the ratio of their lengths will be inversely proportional to the ratio of the absolute values of their thermoelastic coefficients, so that:

L3 am; where L1 and L2 are the lengths, respectively, of the sections 34 and 35, and a1 and as are the thermoelastic coefiicients and where v1 and v2 are the nominal phase velocities of L1 and L2 respectively.

It is seen that this invention provides temperature compensating means for maintaining the resonant frequency of an electromechanical filter end wire relatively constant with temperature changes.

Although this invention has been described with respect to particular embodiments thereof, it is not to be so limited as changes and modifications may be made therein which are within the full intended scope of the invention, as defined by the appended claims.

We claim:

1. A temperature compensated magnetostrictive coupling wire comprising, a first portionformed of a positive thermoelastic coefficient and a second portion formed with a negative thermoelastic coefiicient, said portions having an end-to-end arrangement and vibrating in a longitudinal mode, and the lengths of the first and second portions satisfying the equation:

Luna Lg (1 0 where L1 and L2 are the lengths, respectively, of the portions, a1 and as are the thermoelastic coefficients, and v1 and v2 are the nominal phase velocities of the first and second portions respectively, the total length of said wire being an odd-integer multiple of one-quarter wavelength at its frequency of operation.

2. Means for assisting the temperature compensation of a terminal mechanical impedance of a radio-frequency mechanical filter utilizing plural circular discs fixed in parallel relationship, comprising a magnetostrictive rod member having a length that is an odd-integer multiple of onequarter wavelength in the longitudinal mode of radio-frequency vibration at its frequency of operation,

said rod member having a pair of sections connected endto-end, one of said sections having a positive thermoelastic coefiicient a1, and the other of said sections having a negative thermoelastic coefficient (12, the longitudinal-propagational phase velocity of one Section being In, and the longitudinal-propagational phase velocity of the other section being v2, the ratio of the respective lengths L1 and L2 being related to the thermoelastic coefficients and longitudinal-propagation phase velocities by the expression:

hJia L z i z 3, Means for assisting the temperature compensation of the terminal mechanical impedance of a radio-frequency mechanical filter utilizing plural circular discs fixed in parallel relationship, comprising a magnetostrictive rod member having a large length-to-diameter ratio, said rod member vibrating in a longitudinal mode, said rod member having a p i of sections connected end-t0 end, one of said sections having a positive thermoelastic coeflicient in its longitudinal direction, and the other of said sections having a negative thermoelastic coefficient in its longitudinal direction, the ratio of the lengths of the first to the second portions being equal to the product of the second portions thermoelastic coefiicient and the propagational phase velocity of the first portion divided by the product of the first portions thermoelastic coeflicient and the propagational phase velocity of the second portion.

References Cited in the file of this patent UNITED STATES PATENTS 1,715,324 Haglund May 28, 1929 1,882,397 Pierce Oct. 11, 1932 2,000,025 Ide May 7, 1935 2,486,129 De Walt et a1. Oct. 25, 1949 2,501,488 Adler Mar. 21, 1950 2,551,711 Snoek May 8, 1951 2,572,313 Burns Oct. 23, 1951 2,615,981 Doelz Oct. 28, 1952 2,693,579 Doelz Nov. 2, 1954 

